Enzymes – the story so farEnzymes – the story so farEnzymes are biological catalystsEnzymes are biological catalystsSpeed up reactionsSpeed up reactionsLower the energy needed to make reactions Lower the energy needed to make reactions proceedproceedEnzymes react with substrates - very Enzymes react with substrates - very specificspecificSubstrates have a structure Substrates have a structure complimentarycomplimentary to to the active site of the enzyme (‘lock & key’)the active site of the enzyme (‘lock & key’)Reaction complete = enzyme is unchangedReaction complete = enzyme is unchangedCan help ‘build-up’ or ‘breakdown’ reactionsCan help ‘build-up’ or ‘breakdown’ reactions

Enzymes ctd.Enzymes ctd.Can beCan be intracellular intracellular or or extracellularextracellular

All made of protein, most globularAll made of protein, most globular

Amino acid sequence, and bonding Amino acid sequence, and bonding between them, determines active between them, determines active site shapesite shape

All have an active site

Factors affecting enzymesFactors affecting enzymesTemperature:Temperature:

Increasing temp makes atoms vibrateIncreasing temp makes atoms vibrate

above 40oC, vibrations break above 40oC, vibrations break chemical bonds holding enzyme chemical bonds holding enzyme togethertogether

Structure unravels, active site is lost Structure unravels, active site is lost

= = denatureddenatured

pH:pH:

All enzymes have an optimum pHAll enzymes have an optimum pH

Mostly close to neutral (5-9)Mostly close to neutral (5-9)

exceptions exceptions

- pepsin (2-3)- pepsin (2-3)

- alkaline phosphatase/phosphorylase - alkaline phosphatase/phosphorylase (10) (10)

Factors affecting enzymesFactors affecting enzymesEnzyme concentration:Enzyme concentration:

- enzyme-substrate reaction is - enzyme-substrate reaction is very briefvery brief

- enzyme then moves on to the - enzyme then moves on to the next substrate moleculenext substrate molecule

Turnover Number: Turnover Number:

- no. of substrate molecules which - no. of substrate molecules which an enzyme acts on in a given timean enzyme acts on in a given time

range: 100-4000 per secondrange: 100-4000 per second

Increased enzyme conc. = Increased enzyme conc. = increased reaction rateincreased reaction rate

This will increase at a steady rate This will increase at a steady rate as long as there is substrate as long as there is substrate presentpresent

Factors Affecting EnzymesFactors Affecting EnzymesSubstrate Concentration:Substrate Concentration:

Increasing substrate Increasing substrate conc. will increase conc. will increase reaction rate reaction rate

- more substrates - more substrates binding with active sitesbinding with active sites

After a certain point all After a certain point all the active sites will be the active sites will be filledfilled

Therefore increasing Therefore increasing substrate conc. will no substrate conc. will no longer have an effectlonger have an effect

InhibitorsInhibitorsCompetitiveCompetitive::

- compete directly for - compete directly for enzyme’s active siteenzyme’s active site

- have a structure very - have a structure very similar to that of the similar to that of the substratesubstrate

- active site gets blocked- active site gets blocked

- reaction rate goes - reaction rate goes down as more sites get down as more sites get blocked by inhibitorblocked by inhibitor

- increasing substrate - increasing substrate conc. can return reaction conc. can return reaction rate to normalrate to normal

InhibitorsInhibitors

Non-CompetitiveNon-Competitive::

- Don’t combine with - Don’t combine with active siteactive site

- Attach to another region - Attach to another region on the enzymeon the enzyme

- This results in the active - This results in the active site structure being site structure being altered indirectlyaltered indirectly

e.g cyanide, heavy metalse.g cyanide, heavy metals

- increasing substrate - increasing substrate conc. will not return conc. will not return reaction rate to normalreaction rate to normal

Activation of EnzymesActivation of EnzymesCo-Factor:Co-Factor:

A non-protein substance which A non-protein substance which helps to activate an enzyme helps to activate an enzyme

e.g. Zn, Fe, Cu, Mge.g. Zn, Fe, Cu, Mg

Often helps the substrate to fit Often helps the substrate to fit the active sitethe active site

Some are known as Co-EnzymesSome are known as Co-Enzymes

These are mostly made of These are mostly made of vitaminsvitamins

e.g. Vitamin B - transfers e.g. Vitamin B - transfers Hydrogen during aerobic Hydrogen during aerobic respirationrespiration

Other EnzymesOther EnzymesMany digestive enzymes start off inactiveMany digestive enzymes start off inactive

In the gut they’re activated by In the gut they’re activated by enzyme activatorsenzyme activators

e.g. trypsin & chymotrypsin in the pancreas e.g. trypsin & chymotrypsin in the pancreas

- both protein digesting enzymes- both protein digesting enzymes

- if permanently active, could digest the pancreas itself- if permanently active, could digest the pancreas itself

InactiveInactive ActivatorActivator Active enzymeActive enzyme

trypsinogen + trypsinogen + enterokinaseenterokinase trypsin trypsin

Chymotrypsinogen + trypsin chymotrypsin Chymotrypsinogen + trypsin chymotrypsin + trypsin+ trypsin

Inborn Errors of MetabolismInborn Errors of MetabolismMetabolismMetabolism - sum of all the - sum of all the chemical reactions in the bodychemical reactions in the body

Products of one reaction often Products of one reaction often go into another reaction go into another reaction

All reactions controlled by All reactions controlled by enzymesenzymes

If a genetic fault occurs, the If a genetic fault occurs, the enzymes are not produced enzymes are not produced correctlycorrectly

Intermediate metabolites Intermediate metabolites accumulate and cause accumulate and cause disorders disorders

e.g. albinism, PKU e.g. albinism, PKU

(PKU)